/*
 * Attribute.java July 2006
 *
 * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package wx.xml.simpleframework.xml;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * The <code>Attribute</code> annotation represents a serializable XML
 * attribute within an XML element. An object annotated with this is
 * typically a primitive or enumerated type. Conversion from the
 * attribute to primitive type is done with a <code>Transform</code>
 * object. If a suitable transform can be found then this will convert
 * the attribute string value to an object instance, which can be
 * assigned to the annotated field, or passed to the annotated method.
 *
 * @author Niall Gallagher
 * @see wx.xml.simpleframework.xml.transform.Transformer
 */
@Retention(RetentionPolicy.RUNTIME)
public @interface Attribute {

    /**
     * This represents the name of the XML attribute. Annotated fields
     * or methods can optionally provide the name of the XML attribute
     * they represent. If a name is not provided then the field or
     * method name is used in its place. A name can be specified if
     * the field or method name is not suitable for the XML attribute.
     *
     * @return the name of the XML attribute this represents
     */
    String name() default "";

    /**
     * This is used to provide a default value for the attribute if
     * the annotated field or method is null. This ensures the the
     * serialization process writes the attribute with a value even
     * if the value is null, and allows deserialization to determine
     * whether the value within the object was null or not.
     *
     * @return this returns the default attribute value to use
     */
    String empty() default "";

    /**
     * Determines whether the attribute is required within an XML
     * element. Any field marked as not required will not have its
     * value set when the object is deserialized. If an object is to
     * be serialized only a null attribute will not appear as XML.
     *
     * @return true if the attribute is required, false otherwise
     */
    boolean required() default true;
}
